The invention relates to a method and an apparatus for image rendition using sequential color rendition.
In image rendition with sequential color rendition, distinct color components of the image are rendered not simultaneously but in temporal succession, the rate at which the individual color components succeed one another being so high that the human eye “integrates” the individual color components into a color image.
Apparatuses that utilize such sequential color rendition are for example digital light processing projectors (DLP). Such projectors have a DLP integrated circuit that exhibits a matrix having a multiplicity of individually drivable mirrors. The DLP integrated circuit reflects a beam of light projected from the chip via optics onto a projection surface. The individual mirrors, in dependence on their position, each reflect a part of the incident beam toward the projection surface or away from the projection surface. The DLP integrated circuit is driven by a video signal, a light/dark pattern corresponding to the light/dark pattern of the image to be rendered being mapped onto the light beam reflected by the integrated circuit as a result of the separate driving of the individual mirrors. Lightness gradations can be achieved by virtue of the fact that the individual mirrors oscillate between the positions in which the light beam is reflected toward the projection surface or away from the projection surface.
For the optimal rendition of a color image, three DLP integrated circuits are required to reflect light in each of the three primary colors red, green and blue. The integrated circuits are each driven by a video signal that represents image components each having one of these colors. The monochromatic images generated by the individual integrated circuits are then superimposed by a prism into a polychromatic image.
Due to cost, a single DLP chip is often employed in DLP projectors. The rendition of a color image in this case can be generated by sequential color rendition as follows:
A color wheel, which is transparent by parts for red, green and blue components of a light source, is placed between the light source and the DLP integrated circuit and moved in such that red, green and blue light is cyclically reflected by the DLP integrated circuit. In synchronization with the motion of the color wheel, the DLP integrated circuit is driven by video signals that represent in each case the red, blue and green component of the image to be rendered. As a result, a succession of red, a green and a blue image are generated, and these images are integrated into one image through the physiology of human vision. The basic procedure for image rendition using sequential rendition of individual color components will be explained with reference to FIG. 1 and FIG. 2.
FIG. 1 illustrates two temporally successive images B(k), B(k+1) of an image sequence to be rendered. The images rendered in the example depict an object 10 that is in different positions in the successive images, that is, at a first image position in the first image B(k) and a second position, deviating from the first image position, in the second image B(k+1). If the image frequency is sufficiently high, the impression of a moving object arises as a result.
Suppose that the moving object 10 is a colored object that comprehends color components of all three primary colors, the individual color components possibly differing in intensity. A rendition of this object with the use of sequential color rendition is schematically illustrated in FIG. 2. Suppose the image frequency of the image sequence with images B(k), B(k+1) is f=1/T, T being the temporal interval between the beginning of the rendition of an image and the beginning of the rendition of a subsequent image. Within this duration T, in order to render one of the images B(k), B(k+1) of the image sequence, at least three subimages B1(k), B2(k), B3(k) or respectively B1(k+1), B2(k+1), B3(k+1) are rendered, of which a first subimage depicts the object in only a first color (e.g., in red), a second subimage depicts the object in only a second color (e.g., in green), and a third depicts the object in only a third color, (e.g., in blue). The color intensity of the monochromatic images here corresponds to the color intensity with which the respective color component is present in the color of the object.
The human eye then “blends” these three sequentially rendered subimages into an image that exhibits the colored object at the respective image position.
In the rendition of motion processes, (i.e., in the rendition of objects whose image position changes from image to image of the image sequence) the viewer can receive the impression—even in the case of monochromatic objects—that there are “color fringes” at the edges of the moving objects. The color fringes are especially distinct at the edges of the object that lie perpendicular to the direction of motion; in this connection one speaks of false-color rendition. This impression arises for the user even though the object is rendered at the same location in the image in the successive monochromatic subimages generated in order to render an image.
Therefore, there is a need for a system that renders an image sequence using sequential color rendition, in which the viewer's impression of false-color rendition is reduced.